1. Field of the Invention
The subject invention relates to legged vehicles and toys, and, more particularly, to a resilient leg and its embodiment in a robot for which it provides hopping propulsion.
2. Description of the Invention Background
Human beings and animals have remarkable abilities to walk and run over a wide variety of terrain. In running, as distinct from walking, a machine (or animal) exhibits periods of flight in which contact with the ground is completely lost. Running in general is a dynamic phenomenon where inertial forces are significant, and balance is achieved by active means, not by static equilibrium. Running allows higher speeds than walking, and exploits dynamics to negotiate widely spaced (horizontally or vertically) footholds.
There have been a number of efforts at building running robots. One running robot was a planar one-legged hopper that operated in low effective gravity on an inclined table with thrust provided by a high-force electric solenoid. A succession of machines tested one-leg, two-leg and four-leg designs both in the plane and in three dimensions (3D). Most used a telescoping leg with an internal air spring for compliance, and hydraulic actuators. Some machines have been controlled by the same basic decomposition into three independent linear controllers: forward velocity controlled by foot placement, hopping height controlled by thrust, and pitch controlled by hip torque during stance. This control involved high force and power during stance.
There have been several examples of electrically actuated hoppers. One was constructed with a one-leg electrically actuated planar hopper with a leg constructed from a four bar linkage with a tension spring. Another was built with a one-leg planar hopper with electric motors instead of hydraulics and a metal spring instead of an air spring. Others designed an electrically actuated leg with three revolute joints that used an electric motor coupled with elastic tendons to drive the foot. Others have been designed with an electrically actuated telescoping leg constrained to the vertical. It incorporated a DC motor driving a ball screw in series with a steel spring.
While research on dynamically-stabilized legged locomotion has been completed, previous hopping/running machines have been characterized by the following shortcomings: (i) inefficiency due to losses in the mechanical system and negative work; (ii) the need for large, high-powered actuators for excitation and control of motion; (iii) the requirement for excessive power via off-board power supply; (iv) large body-attitude disturbances and control effort; (v) the inability to perform precise motion control needed for reliable movement over complex terrains; (vi) control complexity; and (vii) vulnerability to damage. In short, previous concepts of running machines have been confined to laboratory environments, and have not been suitable for practical legged locomotion. Thus, there is a need for legged vehicles, which are energy efficient and simple.
There is a further need for a hopper robot that employs a pivoting hip, which minimizes the torque coupling and attitude disturbances during stance.
There is still another need for a hopping robot that is self-righting without the need for computation, actuation, or energy for pitch control.
There is yet another need for a leg that is lightweight and that can be positioned with a low-power actuator such that minimal disturbance is applied to the body.
Another need exists for a leg that has high passive restitution to minimize the energy that needs to be added for each cycle, and to make the impacts relatively repeatable and predictable.
Still another need exists for a hopping, jumping or running robot that stores energy during flight to enable the use of low-powered actuators.